Penn State University assistant football coach Mike McQueary arrives at the Centre County Courthouse to testify in the child sexual abuse trial of former Penn State University assistant football coach Jerry Sandusky in Bellefonte, Pa., Tuesday, June 12, 2012.

Penn State assistant coach Mike McQueary, a key prosecution witness in the trial of fellow football coach Jerry Sandusky, today yelled at a defense attorney when repeatedly pressed about his claim that he saw Sandusky raping a young boy in the team's showers.

McQueary's confrontation with defense lawyer came after he again described finding Sandusky and a boy locked in what he indicated was anal sex, and how he left after making a loud noise and looking at Sandusky, but not speaking to him.

The boy in the showers has never been identified and McQueary's subsequent statements are at the heart of the university's dismissal of school president Graham Spanier, legendary football coach Joe Paterno and criminal charges against two other school officials for not alerting police.

McQueary's testimony is a centerpiece of the state's case against Sandusky and is the first eyewitness account of molestation in the trial. McQueary's eventual statement to investigators, in addition to the alleged victims' own claims, led to Sandusky's arrest on 52 charges of child sex abuse.

McQueary followed to the stand a teenager being identified by ABC News only as Victim 1 whose wrenching story had jurors wiping tears from their eyes. Victim 1's story paralleled the story of Victim 4 who testified Monday that he was abused by Sandusky for years.

McQueary confidently gave the court a detailed description today of hearing "skin-on-skin slapping sounds" when he walked into the shower room of the Penn State football building on a Friday night in 2001 and seeing Sandusky pressed against a young boy in the shower.

He said he saw Sandusky and the boy, about 10 to 12 years old, in the shower with the boy pressed up against the shower wall and Sandusky behind with his arms wrapped around him "in closest proximity I think you can be."

"I see in the mirror Coach Sandusky standing behind boy propped up against the shower, with the showers running, right up against his back with his front, the boy's hands up against the wall," he said. "When I saw them with my own eyes, there was not hard or fast movement. There was subtle movement on defendant's part (in his) mid section."

McQueary said he stepped closer to look directly at the shower, instead of in the mirror, and that Sandusky and the boy separated and looked right at him. He then slammed his locker door shut loudly.

"We looked directly in each other's eye and at that time I left the locker room," McQueary said. "I made the loud noise in an attempt, I think, to say ok someone's here, break it up, please. Again I wasn't thinking quite 100 percent right. I'm used to pressure situations that was more than my brain could handle."

McQueary's statements about what he saw in the shower that night came under scrutiny after the prosecutor's office changed the date of the alleged event from 2002 to 2001, and McQueary's statements to his father, father's friend, and Penn State officials seemed to vary, according to grand jury testimony.

McQueary said that although he described in "vague" terms to his father, his father's friend, and then his Penn State superiors what he saw, he was sure that they knew it was sexual.

"I can tell you that he knew it was extremely sexual in nature, with Jerry involved, and a young boy involved," McQueary said. "I even said, 'Dad, it doesn't take a rocket scientist to figure out what was going on.'"

McQueary, when pressed by Rominger, also said he "made sure Coach Joe knew it was sexual," referring to head coach Joe Paterno.

Rominger tried to show that McQueary had changed his story about what he saw to the people he told.

McQueary, raising his voice on the stand at Rominger, said that if his father's friend contradicted McQueary's account of events, he "would not call him a liar."

McQueary told the lawyer that Rominger was "playing semantics." When asked if he was sure Sandusky saw him in the locker room that night, McQueary said, "I'm a tall man," and "a big red-haired guy, most people see me wherever I go," causing laughter in the courtroom.

Rominger pressed McQueary for details about what he saw, confirming that McQueary never saw genitals or insertion, but McQueary said, "There's no way his genitals were not pressing up against the boy's rear end."

His testimony was the third major account of sexual abuse heard during the trial, and followed the halting, crying testimony of the man known as "Victim 1" this morning, the 18-year-old man who launched the sex abuse investigation into Sandusky.

The teenager wept on the stand today and brought some jurors to tears as he recalled the first time the former Penn State coach allegedly performed oral sex on him, when he was about 12 years old.

"After rubbing, cracking my back and rubbing his hands down back of my shorts, and the blowing on the stomach," he said, pausing to cry, "he put his mouth on my privates. I spaced, I didn't know what to do. With all the thoughts running through my head, I just kind of blacked out and didn't want it to happen. I was froze," he said.

The man, whom ABC News is identifying only as Victim 1 because he's an alleged sex-crime victim, reported the alleged sexual abuse to his mother and his high school in 2008.

The recent high school graduate was the second accuser to testify during the trial, which began Monday in Bellefonte, Pa., 10 miles from Penn State University.

He described meeting Sandusky through Sandusky's charity for underprivileged boys, the Second Mile, and spending time with Sandusky playing sports, doing activities, and sleeping over his house.

Victim 1 described staying In Sandusky's basement bedroom, where a water bed and television were sequestered away from a pool table. It was there that Sandusky began abusing him, he said.

Jury members placed their hands over their mouths or wiped tears away from their eyes as the man testified that Sandusky forced him to perform oral sex.

"lt was back cracking, rolling around in bed, back massages, hands down back of my shorts. The same thing," he said, pausing to cry. "Except this time he sat there and he looked at me and said something along the lines of, 'It's your turn,' and he made me, he made me put my mouth on his privates. In the basement room."

Joseph Amendola, the defense attorney for Sandusky, tried during cross-examination to pick through the accuser's account of events, showing that he told investigators with Children and Youth Services and the state police different timelines for when the oral sex abuse began and ended, and showing that he didn't even mention oral sex to investigators until about eight months into the investigation, when troopers told him there were other young people with similar claims.

The back-and-forth between Amendola and Victim 1 became tense at times, as Amendola asked the accuser to account for multiple differences in his descriptions of abuse to investigators and the grand jury in the past few years. The accuser dismissed Aamendola's suggestion that he was lying, saying it had been difficult to tell people about the abuse, and sometimes he told a "white lie."

Victim 1 threw his head back at one point, covering his face with hands and laughing, before crying, saying 'Stop,' to Amendola. Both the judge and Amendola asked whether the man needed a break from testimony, but he declined.

Victim 1 was adamant that staying at Sandusky's house affected his behavior. "After I started staying with him it [my behavior] changed noticeably. I acted out, I started wetting the bed, I got into fights with people, stuff I would never normally do," he said.

After his testimony, the prosecution called the young man's grandfather and the case worker at Children and Youth Services to whom the case was first referred. The man's grandfather said that his daughter called him once, asking him to break up an argument between Sandusky and Victim 1. He testified that he went to the home, found the pair arguing, and told Victim 1 to go in the house and told Sandusky to leave.

The case worker testified that Victim 1 had not told her of all the allegations during their first meeting, noting that he seemed "nervous and shy" but not like he was lying outright. She described interviewing Sandusky about Victim 1's allegations, and Sandusky admitting to "blowing raspberries" on the boy's stomach, cracking his back, and having the boy sleep at his home "seven to eight times." He denied sexual intent or sexual activity.

Sandusky also denied that he had gone to the boy's school multiple times and pulled him out of class, as Victim 1 had testified earlier. Sandusky told the case worker that he had gone only once to the high school, and pulled the boy from an assembly to ask about helping out at a golf tournament, the woman said.

But Victim 1 said Sandusky showed up at his school often. Once, he and the former football coach were lifting weights and climbing rock walls in the school's recreation facilities when Sandusky pulled the alleged victim down onto him and began rolling around with the boy and blowing on his stomach, Victim 1 said.

"Then the door opened and Joe Miller walked in on me. I felt kind of like a relief that nothing was going to happen in the school," he said.

The court also heard from Miller who told the court he saw them lying on the floor facing one another on wrestling mats.

"I turned to my left and I saw Jerry and (Victim 1) all the way in the back corner, face to face on their sides on a mat, and Jerry propped himself up on one arm and said, 'Hey coach, just working on wrestling moves.' So I didn't think much of it," Miller said. "I thought when I got in the car, that's kind of peculiar, that they'd be on those mats when there are bigger wrestling mats outside, but I thought it's Jerry. Jerry's a saint, so I didn't think anything of it."

Amendola, however, went back over the incident with Victim 1, noting that in his grand jury testimony, Victim 1 said it was "hilarious" when he fell of the rock wall with Sandusky when they were climbing, and that he was "laughing hysterically."

Amendola reiterated that there had been no sexual contact during the incident.

Amendola also hinted that Victim 1 had discussed getting rich by bringing a civil suit against Sandusky, part of the defense strategy Amendola has described since the beginning of the case.

"Have you in presence of your mom ever told anybody that you two were going to become rich after this deal?" he asked.

The accuser said he had not.

"Just so we're clear: you never discussed that you were going to wind up with big house and cars and be rich as result of this case? If someone were to come into court and say that, it wouldn't be true?"

Victim 1 said that maybe he had dreamed about living in a big house or driving a nice car, but had never verbalized it.

Amendola will cross-examine the Children and Youth Services case worker during the afternoon session, and the prosecution might still call more investigators to testify about the investigation into Victim 1's claims.